3.3 GHz BAW Resonators Fabricated on Single Crystal AlN Templates

Aluminum nitride (AlN) piezoelectric films are essential for bulk acoustic wave (BAW) filters operating at super high frequency (SHF). In this paper, the single crystal AlN template is proposed to fabricate highly crystalline AlN piezoelectric films by sputtering. Taking advantage of well-arranged atoms and flat surface of the epitaxial AlN template, the crystalline quality and surface roughness of the subsequent sputtered AlN films are significantly improved. Single crystal AlN BAW resonators are fabricated using wafer bonding and layer transferring processes, with the resonance frequency of 3.3 GHz, quality factor of 865 and effective electromechanical coupling coefficient of 5.0%. Our approach shows the great potential of the single crystal AlN templates to enhance the resonance performance of BAW resonators and filters, thereby facilitating their applications in wireless communication systems operating in the SHF band.